Hardest problem to diagnose in your car?
11-16-2002, 05:17 PM
#1
Rennlist Member
Thread Starter
Hardest problem to diagnose in your car?
The most mysterious problem I've encountered with my cars happened to my S2 cabrio shortly after I bought it in 1999. It had just turned 120,000 miles and in stop and go traffic after extended highway driving, it would cut out intermittently. The car would buck and run very rough until pressing the gas pedal hard enough would get it to keep moving.
The problem was sporadic and I couldn't find a way for the car to produce the symptoms at will, making it hard to diagnose. I asked on the E-mail lists and everyone suggested the DME relay. I changed it and apparently the problem went away. I moved and left the car with a friend for some time. One day he mentioned having the same problem while driving it to get some tires fitted. The gremlins were back.
We took it to my regular shop and my mechanic couldn't figure it out. We then took it to the only place in town that had a Bosch computer that you can plug these cars into to extract fault codes, and it was reading "COE 12 for idle switch short to ground," but they didn't seem to know what to fix.
I asked on the E-mail lists again and the consensus was that the wand in the Air Flow Meter probably wasn't making good contact and needed to be repaired. I went ahead and replaced the whole unit ($400 ).
I then took the car to Florida and everything seemed OK. Put it in storage with another friend, and low and behold, a few weeks later he told me the same symptoms had surfaced while driving.
Now I was really confused. A DME relay and AFM later, the problem was still not fixed, making the car unreliable. I called around and was recommended a reputable shop in Pompano specializing in Porsches. Well, I don't know how they figured it out, but they did. It turns out the problem was caused by a faulty part that is specific to the 944S2 and maybe the S. Don't know about the 951. It's a $35 part located behind the driver side headlight called "ignition control module."
Switched that sucker out and it's been over 7K miles and NO more problems. I wish someone had told me this before I spent $400 on an Air Flow meter I didn't need <img src="graemlins/c.gif" border="0" alt="[ouch]" />
Oh well, that's why I'm posting it here, in case someone else runs into the same problem and can't figure it out either.
The problem was sporadic and I couldn't find a way for the car to produce the symptoms at will, making it hard to diagnose. I asked on the E-mail lists and everyone suggested the DME relay. I changed it and apparently the problem went away. I moved and left the car with a friend for some time. One day he mentioned having the same problem while driving it to get some tires fitted. The gremlins were back.
We took it to my regular shop and my mechanic couldn't figure it out. We then took it to the only place in town that had a Bosch computer that you can plug these cars into to extract fault codes, and it was reading "COE 12 for idle switch short to ground," but they didn't seem to know what to fix.
I asked on the E-mail lists again and the consensus was that the wand in the Air Flow Meter probably wasn't making good contact and needed to be repaired. I went ahead and replaced the whole unit ($400
).I then took the car to Florida and everything seemed OK. Put it in storage with another friend, and low and behold, a few weeks later he told me the same symptoms had surfaced while driving.
Now I was really confused. A DME relay and AFM later, the problem was still not fixed, making the car unreliable. I called around and was recommended a reputable shop in Pompano specializing in Porsches. Well, I don't know how they figured it out, but they did. It turns out the problem was caused by a faulty part that is specific to the 944S2 and maybe the S. Don't know about the 951. It's a $35 part located behind the driver side headlight called "ignition control module."
Switched that sucker out and it's been over 7K miles and NO more problems. I wish someone had told me this before I spent $400 on an Air Flow meter I didn't need <img src="graemlins/c.gif" border="0" alt="[ouch]" />
Oh well, that's why I'm posting it here, in case someone else runs into the same problem and can't figure it out either.
11-16-2002, 05:40 PM
#2
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The DME design of the 944S cars is a bit different than the "regular" 944 DME's.
As you found out they decided to put an isolator between the DME brain and the high voltage coil. This interface takes the coil firing info from the DME and makes quite a nice square wave signal to the coil. I figure that the coil has a bit more "spark" or Porsche decided that it had replaced too many DME's and that the isolator was cheaper.
With a bit of wiring anyone with a DME like ours can put this interface/isolator on their car. I would strongly recommend this for those that have used an after market "hotter" coil.
If you have the factory manuals the testing procedure for the S's is in the back of the first engine section. This component is listed in that section.
As you found out they decided to put an isolator between the DME brain and the high voltage coil. This interface takes the coil firing info from the DME and makes quite a nice square wave signal to the coil. I figure that the coil has a bit more "spark" or Porsche decided that it had replaced too many DME's and that the isolator was cheaper.
With a bit of wiring anyone with a DME like ours can put this interface/isolator on their car. I would strongly recommend this for those that have used an after market "hotter" coil.
If you have the factory manuals the testing procedure for the S's is in the back of the first engine section. This component is listed in that section.
